The present invention relates to a position sensor for an electromagnetic actuator which is used in various systems for a vehicle and detects a position of a shaft to be detected which moves axially in synchronization with a movable shaft of the electromagnetic actuator.
To meet recently-increasing requirement for improving fuel efficiency of a vehicle, various measures directed toward the improvement of the fuel efficiency have been studied. Among them, a high voltage of a battery enables an electromagnetic actuator such as a linear solenoid or the like to have both a great driving force and miniaturization. Consequently, the electromagnetic actuator, which having a higher efficiency to various kinds of electronics systems than a mechanical actuator, has been studied. In order to apply the electromagnetic actuator to these electronics systems, the position of a movable shaft must be controlled accurately. Accordingly, a position sensor becomes important for the accurate position detection of the movable shaft.
With reference to FIG. 7, a conventional position sensor (disclosed in Japanese Patent Laid-Open No. 5-264326) for the electromagnetic actuator will be hereinafter described.
FIG. 7(a) is a perspective general view of the conventional position sensor for the electromagnetic actuator.
FIG. 7(b) shows a cross section taken along arrow Cxe2x80x94C of the sensor.
FIG. 7(c) is a perspective view detailing a relationship between a magnetoelectric transducer and a magnetic field generator of the sensor.
In FIGS. 7(a), 7(b) and 7(c), reference numeral 100 denotes a shaft to be detected. Reference numeral 100a denotes a guide groove formed in a longitudinal direction of the shaft 100. Reference numeral 110 denotes a magnet 110 polarized magnetically in a thickness direction. Reference numeral 120 denotes a magnetic plate made of a permalloy shaped like an isosceles triangle. Reference numeral 130 denotes a magnetic field generator including the magnet 110 and the magnetic plate 120 attached together in their respective longitudinal direction matching together. Reference numeral 140 denotes a magnetoelectric transducer. Reference numeral 310 denotes a flat surface of the shaft 100. Reference numeral 320 denotes a slider including an insulating material engages with the guide groove 100a, for sliding smoothly relative to the shaft 100. The magnetoelectric transducer 140 provided at the slider 320 is mounted in parallel with the magnetic field generator 130 provided on the flat surface 310 of the shaft 100.
An operation of the conventional sensor will be explained below.
The shaft 100 is displaced relative to the slider 320 (in the direction of an arrow D in FIG. 7(a)), the magnetic plate 120 is opposed to the magnetoelectric transducer 140 accordingly with various widths. Consequently, an electric field sensed by the magnetoelectric transducer 140 varies in strength accordingly, thus enabling the sensor to detect the position of the shaft 100.
The conventional position sensor described above, however, has the following problem. The conventional position sensor for the electromagnetic actuator has a contacting portion functioning as a guide for preventing the magnetoelectric transducer 140 from rotating about an axis of the magnetic field generator 130. The sensor, if being used over a long period of time, has the contacting portion wearing unevenly and causing backlash, which makes the sensor generate an unstable output.
The present invention addresses the problem discussed above and aims to provide a position sensor for an electromagnetic actuator. The position sensor is capable of accurate non-contacting position detection, not restricting rotation of a shaft to be detected about an axis of the shaft.
To solve this problem, the position sensor of the present invention includes: a first magnet being fixed to the shaft to be detected which moves axially in synchronization with a movable shaft of the electromagnetic actuator, and having a first polarity vector parallel to the axis of the shaft; a second magnet being disposed opposite to the first magnet and having a second polarity vector crossing the first polarity vector substantially orthogonally three-dimensionally; and a magnetoelectric transducer being disposed over the second magnet and having a magnetosensitive axis substantially orthogonal to the first and second polarity vectors. The magnetoelectric transducer generates an output responsive to an axial movement of the shaft. With this configuration, the position sensor for the electromagnetic actuator can detects the position accurately with no contact, not restricting the rotation of the shaft about the axis of the shaft at all.